Copper particle clusters and powder containing the same suitable as conductive filler of conductive paste

Abstract

Copper particle clusters constituting a powder suitable for making a conductive paste are provided that are individually composed of not fewer than two and not more than 20 unit particles joined through neck portions. A conductive paste made from the powder is excellent in conductivity. A conductive filler for conductive paste is provided that consists essentially of a mixture of copper particle clusters A individually composed of two or more unit particles joined through neck portions and spherical metallic particles B of smaller diameter than the particles A. A conductive paste made from the filler is low in viscosity and excellent in conductivity.

1. A process for producing a copper powder including copper particle clusters comprising:
 a step of precipitating copper hydroxide by reacting an aqueous solution of a copper salt and an alkali under an atmosphere of an oxygen-containing gas to obtain a suspension containing copper hydroxide, 
 an intermediate reduction step effected by adding a reducing agent to the suspension to reduce the copper hydroxide to cuprous oxide, 
 a step of blowing an oxygen-containing gas into the suspension containing cuprous oxide, and 
 a final reduction step of reducing the cuprous oxide in the suspension to metallic copper using a reducing agent. 
 
     
     
       2. A process according to  claim 1 , wherein the copper hydroxide precipitating step is conducted in an aqueous solution of an Fe concentration of not greater than 50 ppm.